1. Field of the Invention
The present invention relates to a method and an apparatus for continuously casting a uranium rod by melting a metallic substance reduced from nuclear spent fuels, and more particularly to a method and an apparatus for continuously casting a uranium rod so that impurities generated in melting the metallic substance reduced from nuclear spent fuels are easily removed, the molten metal is easily degassed, the oxidation of uranium is prevented, and residue of the molten metal does not remain in a crucible.
2. Description of the Related Art
Generally, nuclear spent fuels generated during nuclear power generation still comprise a great quantity of uranium. In order to effectively store and manage the nuclear spent fuels, the nuclear spent fuels are reduced to a metallic substance without any separation and purification, and then cast into a uranium rod for storage.
By casting the metallic substance reduced from nuclear spent fuel into a uranium rod, the nuclear spent fuel can be easily stored and treated, and recycled as a nuclear fuel, thereby creating an economic benefit.
In order to achieve such economic benefit, a method for continuously casting the metallic substance reduced from nuclear spent fuels into the uranium rods is used. For conventional continuous casting, a method and an apparatus for melting a uranium ingot and degassing the molten uranium in an air-sealed chamber with a designated degree of vacuum and then extracting a uranium rod from the air-sealed chamber by a start rod and a driving roller are proposed.
However, in the conventional continuous casting method and apparatus, since the cast uranium rod is pulled down from the bottom of the air-sealed chamber, it is very difficult to maintain the designated degree of vacuum of the air-sealed chamber. As a result, the uranium rod around the bottom surface of the air-sealed chamber, in which the vacuum is reversed, is easily oxidized.
In order to solve the aforementioned problem, another continuous casting method and its apparatus are proposed. Herein, the air-sealed chamber is filled with an inert gas, and then the continuous casting of a uranium rod is carried out.
In the inert gas atmosphere, the molten metal cannot be sufficiently degassed, thereby manufacturing a poor quality uranium rod.
Further, in order to prevent the oxidation of uranium, a great quantity of inert gas must be continuously supplied to the air-sealed chamber, thereby wasting the inert gas.
In order to solve the aforementioned problems according to the use of the inert gas, another continuous casting method and its apparatus are proposed. Herein, the nuclear spent fuel is melted in the air-sealed chamber under the vacuum condition, and the uranium rod is pushed out from the top of the air-sealed chamber by the high-pressure inert gas.
In this continuously casting method and apparatus, since the uranium rod is pushed upward by the high pressure, the degassing and the prevention of oxidation are possible. However, the molten metal is not completely exhausted. That is, the residue of the molten metal remains in the air-sealed chamber.
The residue of the molten metal in the air-sealed chamber is easily hardened. As a result, in order to reuse the air-sealed chamber, a step for removing the hardened residue of the molten metal is necessary. Further, since workers cannot be easily close to the air-sealed chamber containing the radioactive residue of the molten metal, in order to reuse the continuous casting apparatus, additional steps and much time are required, thereby drastically shorting a recycle rate of the continuous casting apparatus.
Moreover, the workers removing the radioactive substance, i.e., the residue of the molten metal, are exposed to the environmental contaminants such as the radioactivity, thereby being unsafe to perform.
This continuous casting apparatus does not comprise a shielding chamber. Therefore, when the cast uranium rod is pushed out from the top surface of the air-sealed chamber, noxious gas exhausted along with the uranium rod cannot be properly sucked and the radioactivity cannot be shielded.
Further, the above-described continuous casting apparatus comprises a mold serving as a straw for sucking the molten metal within the crucible. The mold in the crucible must have a sufficient length. The outer surface of the uranium rod molded via the long mold is easily damaged, thereby increasing a defective ratio of uranium rods.
In order to suck and pull up the uranium rod from the molten metal within the crucible, the lower part of the mold must be put into the molten metal. Therefore, the repeated insertion of the mold into the molten metal accumulates the damage of the mold, and the mold is contaminated with radioactivity.
In order to minimize the residue of the molten metal in the crucible, the crucible must be moved upward within the air-sealed chamber under high temperature and high pressure conditions, thereby causing breakdowns or failures of the apparatus and break-out of the cast uranium rod due to the non-uniform suction.
Therefore, the present invention provides a method for continuously casting a uranium rod, in which the impurities generated in melting a metallic substance reduced from a nuclear spent fuel (that is a highly radioactive substance) is easily removed, the molten metal is easily degassed, the oxidation of uranium is prevented, and residue of the molten metal does not remain in the crucible.
The present invention provides a method for continuously casting a uranium rod, in which the inert gas filled in the air-sealed chamber has a constant pressure similar to atmospheric pressure.
The present invention provides a method for continuously casting a uranium rod, in which the cast uranium rod is continuously pulled down without being breakout.
The present invention provides a method for continuously casting a uranium rod, in which the cast uranium rod molded via a mold is cooled at a constant temperature.
The present invention provides a method for continuously casting a uranium rod, in which the first cooled uranium rod is secondarily and completely cooled by the inert gas prior to being exhausted into the shielding chamber.
The present invention provides a method for continuously casting a uranium rod, in which a noxious gas exhausted along with the uranium rod is completely sucked.
The present invention provides a method for continuously casting a uranium rod, in which the exhausted uranium rod is cut without interfering with the continuous casting process.
The present invention provides a method for continuously casting a uranium rod, in which the cut uranium rod is transferred and stored.
The present invention provides an apparatus for continuously casting a uranium rod, in which the impurities generated in melting a metallic substance reduced from a nuclear spent fuel (that is a highly radioactive substance) are easily removed, the molten metal is easily degassed, the oxidation of uranium is prevented, and residue of the molten metal does not remain in the crucible.
The present invention provides an apparatus for continuously casting a uranium rod, in which a region including a driving roller under the air-sealed chamber is shielded from the radioactivity generated from the cast uranium rod.
The present invention provides an apparatus for continuously casting a uranium rod, in which the uranium rod within the mold is not breakout due to the sudden temperature difference but is continuously pulled down.
The present invention provides an apparatus for continuously casting a uranium rod, in which the thermal losses in the crucible and the mold are prevented by an adiabatic material.
The present invention provides an apparatus for continuously casting a uranium rod, in which the uranium rod, molded via the mold and pulled down from the mold, is firstly cooled.
The present invention provides an apparatus for continuously casting a uranium rod, in which a start rod inserted into the crucible is stably supported and fixed.
The present invention provides an apparatus for continuously casting a uranium rod, in which the nuclear spent fuel is introduced from the upper part of the air-sealed chamber into the crucible.
The present invention provides an apparatus for continuously casting a uranium rod, in which the start rod is not easily melted by the molten uranium, and is easily assembled and dissembled.
The present invention provides an apparatus for continuously casting a uranium rod, in which the uranium rod is easily cut without interfering with the continuous casting process.
The present invention provides an apparatus for continuously casting a uranium rod, in which the inert gas filled in the air-sealed chamber is automatically exhausted when a pressure of the chamber is greater than a designated pressure.
The present invention provides an apparatus for continuously casting a uranium rod, in which the air-sealed chamber is easily opened and closed.
The present invention provides an apparatus for continuously casting a uranium rod, in which the first cooled uranium rod is secondarily and completely cooled by the inert gas prior to being exhausted into the shielding chamber.
The present invention provides an apparatus for continuously casting a uranium rod, in which the noxious gas exhausted along with the uranium rod, is locally and completely sucked.
The present invention provides an apparatus for continuously casting a uranium rod, in which the crucible, the mold, and the cooling section are supported within the air-sealed chamber.
The present invention provides an apparatus for continuously casting a uranium rod, in which the uranium rod is cooled at a constant temperature by the cooling section.
The present invention provides an apparatus for continuously casting a uranium rod, in which the cut uranium rod is cut and then transferred.
The present invention provides an apparatus for continuously casting a uranium rod, in which the uranium rod pulled down via the mold and the cooling section within the air-sealed chamber is visually inspected by a worker with naked eyes.
The present invention provides an apparatus for continuously casting a uranium rod, in which the cut and transferred uranium rod is stored in the lower shielding chamber.
In accordance with one aspect of the present invention, the above and other objects can be accomplished by the provision of a continuous casting method for melting a metallic substance reduced from a nuclear spent fuel and casting the molten metal into a uranium rod, comprising: a vacuum melting step for forming a vacuum condition in an air-sealed chamber provided with a crucible and melting the metallic substance reduced from nuclear spent fuel introduced into the crucible under the vacuum condition by heating the crucible; an inert gas filling step for reversing the vacuum condition of the air-sealed chamber and filling the air-sealed chamber with an inert gas; a uranium rod pulling down step for pulling down the uranium rod from the crucible filled with the molten metal in the inert gas atmosphere by downwardly moving a start rod inserted into a mold by a driving roller; a uranium rod cooling step for cooling the pulled out uranium rod by a cooling jacket installed around the uranium rod; and a uranium rod exhausting step for exhausting the cooled uranium rod into a hermetically sealed shielding chamber.
The continuous casting method, between the inert gas filling step and the uranium rod pulling down step, may further comprise a pressure maintaining step for maintaining a constant pressure of the air-sealed chamber by exhausting the inert gas injected into the air-sealed chamber in case the inert gas is in a high pressure state.
Further, in the uranium rod pulling down step, the uranium rod may be pulled down by repeating the pulling out of the start rod and the uranium rod within a designated period of time and then the stopping of the pulling-out of the start rod and the uranium rod within another designated period of time.
Further, the continuous casting method, between the uranium rod pulling down step and the uranium rod cooling step, may further comprise a cooling water volume controlling step for sensing a temperature of the mold and then controlling a cooling water volume according to the sensed temperature of the mold.
Further, the continuous casting method, between the uranium rod-cooling step and the uranium rod-exhausting step, may further comprise a gas-cooling step for secondarily cooling the uranium rod firstly cooled by the cooling water by the inert gas.
Further, the continuous casting method, after the uranium rod exhausting step, may further comprise a noxious gas sucking step for completely sucking a noxious gas exhausted along with the exhaustion of the uranium rod by a local suction device installed around the uranium rod pulled down into the shielding chamber.
Further, the continuous casting method, after the uranium rod exhausting step, may further comprise a uranium rod cutting step for cutting the uranium rod exhausted from the shielding chamber to the outside.
Further, the continuous casting method, after the uranium rod-cutting step, may further comprise a transferring and storing step for transferring the cut uranium rod and storing the transferred into a storage shed.
In accordance with another aspect of the present invention, there is provided a continuous casting apparatus, in which a crucible surrounded with a high frequency induction coil is disposed within an air-sealed chamber, a mold and a cooling section are successively disposed under the crucible, a driving roller is disposed below the air-sealed chamber, thereby casting and pulling down a uranium rod via the mold using a start rod, comprising: a vacuum generating section for forming a vacuum in the air-sealed chamber, including an air exhaust pipe disposed on a side of the air-sealed chamber so as to be connected to the air-sealed chamber and a suction pump formed on the air exhaust pipe; an inert gas generating section for establishing an inert gas atmosphere in the air-sealed chamber, including an inert gas injection pipe disposed on the other side of the air-sealed chamber and an inert gas exhaust pipe disposed on the lower surface of the air-sealed chamber and provided with a switching valve; and a switching section for opening and closing a route for moving the uranium rod pulled down by the driving roller under the air-sealed chamber.
Further, the continuous casting apparatus may further comprise a shielding chamber including a hermetic connection pipe provided with a passage for the uranium rod under the air-sealed chamber and the switching section formed on the lower surface of the hermetic connection pipe, wherein the driving roller and the lower part of hermetic connection pipe are surrounded by the shielding chamber.
Further, the mold may comprise: a mold body including an inserting part inserted into a hole of the lower surface of the crucible, a heat insulating part formed integrally with the lower part of the inserting part, and an exhausting part vertically formed integrally with the lower part of the heat insulating part; a molding hollow vertically formed on the center of the mold body; and a silicon nitride tube attached to an inner wall of the molding hollow.
Further, the crucible and the mold may be surrounded with an adiabatic material made of graphite.
Further, the cooling section may comprise a cooling jacket surrounding the lower part of the mold, and cooling water flow tubes formed within the cooling jacket so as to provide cooling water.
Further, a start rod-supporter may be formed on a surface of the passage within the hermetic connection pipe, and a supporting rod may be disposed on a designated position of the side surface of the start rod-supporter and hydraulically operated.
Further, a switching door opened and closed by a hydraulic cylinder may be formed on the upper surface of the air-sealed chamber.
Further, the start rod may comprise an upper start rod including a fixing hole on its lower surface and a removable part formed on the upper surface of the fixing hole, and a lower start rod including on its upper surface a fixing protrusion inserted into the fixing hole of the upper start rod and fixed to the removable part of the upper start rod.
Further, the continuous casting apparatus may further comprise: a lower shielding chamber formed on the lower surface of the driving roller; and a cutting section including a fixing part for fixing the uranium rod pulled down into the lower shielding chamber, upper and lower cutting blades for cutting the uranium rod under the fixing part, and a spring for elastically returning the fixing part to its former position so as to repeatedly cut the uranium rod.
Further, the switching valve may comprise a high pressure-down pipe in a rectangular shape connected to the inert gas exhaust pipe within the shielding chamber and connected to an external device, and a weight switching part opened and closed by a conical bob with a designated weight formed on a tip of the inert gas exhaust pipe within the high pressure-down pipe.
Further, the switching section may comprise a hydraulic actuator installed on the lower surface of the hermetic connection pipe and hydraulically operated, and a lid operated by the hydraulic actuator.
Further, the continuous casting apparatus may further comprise a gas cooling section including an inert gas injection pipe disposed within the hermetic connection pipe, and a gas exhaust pipe formed on the lower surface of the hermetic connection pipe.
Further, the continuous casting apparatus may further comprise a local suction section including a suction device disposed near the switching section within the shielding chamber and having a plurality of suction holes, a flow tube with its one terminal connected to the back surface of the suction device, and a suction pump connected to the other terminal of the flow tube and formed outside the shielding chamber.
Further, the continuous casting apparatus may further comprise a supporting section including a supporter formed on the lower surface of the cooling jacket and provided with a vertical through hole at its center, and a bearing plate centrally supporting the supporter and disposed within the air-sealed chamber.
Further, the continuous casting apparatus may further comprise a cooling water volume controlling section controlling the cooling section to cool the uranium rod to a constant temperature and including thermocouples disposed within the mold, and a controller for controlling a cooling water volume of the cooling jacket according to the temperature sensed by the thermocouples.
Further, the continuous casting apparatus may further comprise a transferring section including a fracture part for fracturing the cut uranium rod formed under the cutting section, and a horizontal transferring part for horizontally transferring the cutted uranium rod.
Further, the continuous casting apparatus may further comprise a visual inspection section including a quartz pipe vertically formed on the vertical through hole under the supporter, and a transparent window formed on the air-sealed chamber corresponding to the quartz pipe.
Further, the continuous casting apparatus may further comprise a storage shed for storing the transferred uranium rod near the transferring section.